JP2006216179A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which reduces crosstalk in a focus servo using an astigmatism method, thereby improving the reliability of the focus servo. <P>SOLUTION: A hologram pattern of astigmatism formed in each divided region of a diffraction element 2 included in the optical pickup is set so that a direction L1 of astigmatism of a first region and a third region intersects a direction L2 of astigmatism of a second region and a fourth region, where the first, second, third and fourth regions are divided regions obtained by division with a division line M parallel to a radial direction and a division line N parallel to a track direction, and are represented by 2A, 2B, 2C, and 2D, respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup that is used for an information recording medium such as an optical disk and optically records and reproduces information.

  So far, optical pickups having a configuration in which astigmatism is applied to return light from an information recording medium such as an optical disk using a hologram element and a focus servo signal is generated by an astigmatism method have been disclosed so far. (See Patent Documents 1 and 2). FIG. 7 shows a schematic configuration diagram of an optical pickup of the above method. This optical pickup includes a laser 101 as a light source, a hologram element (diffraction element) 102, a collimator lens 103, an objective lens 104, and a light receiving element 106. In the figure, the X-axis direction represents a direction parallel to the track of the disk 105, and the Y-axis direction represents the radial direction of the disk 105.

  The light beam 300 emitted from the laser 101 passes through the hologram element 102, passes through the collimator 103 and then the objective lens 104, and is condensed on the optical disk 105. The reflected light from the optical disk 105 passes through the objective lens 104 and the collimator 103 and is guided onto the hologram element 102.

  The hologram element 102 is for guiding the return light from the optical disk 105 to the light receiving element 106, and a hologram is formed on the hologram element 102. The return light is divided into two semicircles by a dividing line along the radial direction (Y direction) by the hologram.

  FIG. 8 is a diagram showing a planar positional relationship between the hologram element 102 and the light receiving element 106. Referring to FIG. 8, the light receiving element 106 includes two two-divided detectors separated by a separation band 108. Astigmatism is generated in each semicircular portion of the hologram element 102 so that the light spots of the divided light from the hologram element are formed as semicircles rotated by 90 degrees at different positions on the detector 106. A hologram pattern is formed. In FIG. 8, the direction of the arrow H1 represents the direction of astigmatism, and is a direction of 45 degrees with respect to the dividing line M (Y direction: radial direction).

  Here, the astigmatism direction H1 is the direction along the axis where the light spot is reversed when the original light spot and the light spot in the circle of least confusion are compared. The detector 106 is arranged at a position where the light spot is a minimum circle of confusion, and FIG. 8 shows the light beam spot just in a focused state. The semicircular light spots are separated by the separation band 108 and detected by the two-divided detectors 106A and 106B having the boundary line Ld in the same direction as the light traveling direction. The center of the semicircle of the light spot is set to be the position of the boundary line Ld.

In the optical pickup, a spot position signal on the optical disk is obtained by the following calculation. A focus error signal (FES) that is a position detection signal in the optical axis direction, push-pull (PP) that is a position detection signal in the radial direction, or DPD (Differential Phase Detection) signals are A, B, C, and D, respectively. Assuming that the signal intensities detected in the respective light receiving element regions are I _A , I _B , I _C and I _D , FES = (I _A + I _D ) − (I _B + I _C ), PP = (I _A + I _C ) − (I _B + I _D ), DPD = Phase ((I _A + I _D ) − (I _B + I _C )). Phase in the DPD indicates that the phases of the signals are compared. The information (RF) recorded on the optical disc is generated by the calculation of RF = I _A + I _B + I _C + _ID .

  As described above, in the astigmatism method, the above-described three position control signals can be obtained with a simple configuration in which light divided into two and each of them are detected by a two-divided detector. In the case of the knife edge method, which is another focus error signal detection method, the push-pull signal must be generated from a part of the light beam under the condition that the number of detection areas is the same (four), but astigmatism. The method has the advantage that it can be generated using all light beams.

  Next, the principle of FES detection by the above astigmatism method will be described. FIG. 9 shows how the beam shape on the light receiving element changes in accordance with the change in the focus state of the light beam on the optical disk. FIG. 9 shows the state of the detector 106A shown in FIG. 8, and the state shown in FIG. 9C is a light spot in the in-focus state. In a state where the defocus amount is sufficiently large in the plus (+) direction ++ (FIG. 9A) or in a state where the defocus amount is sufficiently large in the minus (−) direction (FIG. 9E), light is not emitted. The intensity distribution of the spot is biased to one side of the two-divided detector. Further, in FIGS. 9A and 9E, the distribution positions are reversed across the boundary line Ld. As the in-focus state approaches, the beam shape changes and the intensity distribution moves slightly beyond the boundary line Ld to the other detector side. When in the in-focus state, both detectors sandwiching the boundary line Ld The intensity distributions of are just equal. The shape of the light spot is a shape obtained by rotating a semicircle on the hologram by 90 degrees.

  The sign of FES based on the above calculation is FES> 0 when in the state of FIGS. 9 (e) and 9 (d), FES = 0 at the focal point of FIG. 9 (c), FIG. When in the state (a), FES <0. In this way, the defocus state can be known from the sign and magnitude of the FES signal.

On the other hand, the push-pull pattern appears on the hologram 102 with a straight line passing through the optical axis and parallel to the track direction (X direction) as shown in FIG. Rotates and appears across the detector boundary. Therefore, a push-pull signal can be generated by taking the difference between the outputs of the two-divided detectors.
Japanese Unexamined Patent Publication No. 63-13134 JP 2003-173550 A

  In the astigmatism method, there is a problem that when the position of the light beam on the detector is misaligned, the track cross signal component is mixed into the focus servo signal (crosstalk). The cause of the occurrence will be briefly described as follows.

FIG. 10 shows a light spot on the detector 106 in the defocused state. FIG. 10A shows the case where the center position of the light spot is on the boundary line Ld of the two-divided detector, and FIG. 10B shows the case where the center G is shifted from the boundary line Ld. In FIG. 10A, the push-pull component that was in the A region in the detector 106A in the in-focus state is partially mixed in the B region side in the defocused state. On the other hand, in the detector 106B, the reverse-phase push-pull component that was on the D region side is partially mixed on the C region side, and the mixing amount is almost the same as that on the detector 106A side. In each of the signal outputs (I _A + I _D ) and (I _B + I _C ), the push-pull component is canceled regardless of the radial position of the light beam on the disk.

On the other hand, when the center position G deviates from the boundary line Ld as shown in FIG. 10B, the amount of push-pull components to be mixed is different, so that (I _A + I _D ) and (I _B + I _C ) In each signal output, the push-pull component is not sufficiently canceled out. For this reason, when the light beam moves in the radial direction on the disk, an alternating current (AC) component (track cross signal) is generated in the FES signal as shown in FIG. In particular, when this noise component becomes large near the in-focus position, the focus servo becomes unstable.

  In particular, in a disk with a large track pitch, such as a DVD-RAM, the push-pull component area is large in the return light from the optical disk, so that even a slight light spot position deviation on the detector tends to appear. Become. Further, in a hologram laser in which adjustment of the beam spot on the detector is performed only by rotating the hologram element and adjusting the X and Y directions, the light spot position on the detector is likely to be shifted. Therefore, there is a problem that the track cross signal that leaks into the focus signal also increases.

  An object of the present invention is to provide an optical pickup in which the cross servo is reduced and the reliability of the focus servo signal is improved in the focus servo signal by the astigmatism method.

  An optical pickup according to the present invention is disposed between a light source that emits a light beam, a condensing element that condenses the light beam on an optical recording medium, and the light source and the condensing element, and reflects from the optical recording medium. A diffractive element that divides light into a plurality of light beams, and a detection unit that includes a light receiving element that receives the light beam divided by the diffractive elements. In this optical pickup, the diffractive element has a plurality of divided regions each formed with a hologram pattern that generates astigmatism, and the plurality of light beams diffracted in each region are at different positions on the detection unit. A direction of astigmatism in which a hologram pattern is generated in one region among a plurality of regions of the diffraction element that forms a light spot is a direction of astigmatism in which a hologram pattern is generated in at least one of the other regions. It is characterized by being different. Here, as described above, the direction of astigmatism is the direction along the axis where the light spot is reversed when the original light spot and the light spot in the circle of least confusion are compared.

  Another optical pickup according to the present invention includes a light source that emits a light beam, a light condensing element that condenses the light beam on the optical recording medium, and the light source and the light condensing element. A diffractive element that diffracts the reflected light from the light into a plurality of light beams, and a detector having a light receiving element that receives the plurality of light beams diffracted by the diffractive element. In this optical pickup, the diffractive element has four hologram patterns that respectively generate astigmatism corresponding to four regions divided by two intersecting dividing lines, and the four hologram patterns are: The detection unit diffracts so as to form four light spots separated from each other in a focused state.

  In the latter optical pickup, any hologram pattern may be used as long as the light spot forms a light spot separated from each other for each hologram pattern as long as the hologram pattern generates astigmatism. In addition, when the four light spots separated from each other are four light spots formed radially from the center, the light spots may be contacted in the form of dots at the center if they do not contact at the diameter.

  By using the optical pickup according to the present invention, the FES crosstalk is suppressed even when the light spot on the detector has a spot shift in the track direction, that is, in the direction perpendicular to the boundary line of the two-divided detector. Therefore, more stable focus servo can be performed.

  Further, when the hologram element is configured to impart polarization characteristics, the presence or absence of diffraction can be changed, so that it is possible to suppress the light amount loss of the light beam that reaches the information recording medium. For this reason, since an intense light beam can be applied to an information recording medium such as an optical disk, information can be recorded on the optical disk at high speed. Further, when the light source and the detector are integrated, the optical pickup can be downsized.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of the optical pickup according to the present embodiment. The optical pickup according to the present embodiment includes a semiconductor laser (light source) 1, a hologram element (dividing unit) 2, a collimating lens 3, an objective lens (condensing unit) 4, and a light receiving unit (detecting unit) 6. The semiconductor laser 1 irradiates the optical disc 5 with laser light. The semiconductor laser 1 emits a laser beam (light beam) 7 having a wavelength of 650 nm, for example. Note that the wavelength of the light beam 7 emitted from the semiconductor laser 1 is not particularly limited, and may be, for example, 750 nm. The collimating lens 3 converts light emitted from the light source into parallel light. The collimating lens 3 converts the light reflected from the optical disk 5 and passed through the objective lens 4 into condensed light.

  The objective lens 4 focuses the light beam converted into parallel light by the collimating lens 3 on the optical disk 5. Further, the light beam reflected by the optical disk 5 passes through the objective lens 4 and the collimating lens 3 and enters the hologram element 2. The directions indicated by X and Y in the figure are the track direction and the radial direction, respectively. The radial direction Y indicates the radial direction when the optical disk 5 is an optical disk such as a DVD, for example, and the track direction X is a direction parallel to the track of the disk orthogonal to the radial direction. The focus direction is a direction parallel to the optical axis of the light beam guided to the objective lens 4 and is perpendicular to the recording surface on which information on the optical disk 5 is recorded.

  The hologram element (diffraction element) 2 divides (diffracts) the light beam reflected by the optical disk 5 and passed through the objective lens 4 and the collimating lens 3 and guides it to the light receiving element. The hologram element 2 is divided into two regions by a straight line M along the radial direction, and the light beam reflected from the optical disk 5 and passed through the objective lens 4 is divided by each divided region and is incident on the light receiving unit 6. . A focus error signal and a tracking error signal are generated based on the received signal. The detailed configuration of the hologram pattern (divided pattern) of the hologram element 2 will be described later.

  The light receiving unit 6 has a plurality of light receiving elements, detects the light beam separated by the hologram element 2 and converts it into an electrical signal. The light receiving unit 6 detects the light intensity of the received light beam. The detailed configuration of the light receiving unit 6 will be described later.

  An optical disc (optical recording medium) 5 has a recording layer for recording information. Examples of the optical disc 5 include CDs and DVDs.

  Next, the light beam emitted from the semiconductor laser 1 will be described. The light beam emitted from the semiconductor laser 1 is diffracted by the hologram element 2. Of the diffracted light beam, the 0th-order diffracted light is condensed on the optical disk 5 via the collimating lens 3 and the objective lens 4. The light beam guided to the optical disk 5 is reflected by the recording layer of the optical disk 5. Then, the light beam reflected by the optical disk 5 is guided to the hologram element 2 through the objective lens 4 and then the collimating lens 3. The light beam applied to the hologram element 2 is divided into a plurality of light beams by the hologram element 2 and guided to the light receiving element 6.

  FIG. 2 is a plan view showing a planar positional relationship between the hologram pattern of the hologram element 2 according to the present embodiment and the light receiving unit 6 to which the light beam irradiated by the hologram pattern is irradiated. Here, the hologram element 2 of the present embodiment will be described in detail. The hologram element 2 in the present embodiment is disposed between the semiconductor laser 1 and the objective lens 4. As shown in FIG. 2, the hologram element 2 has a hologram pattern including two divided portions 2A and 2B separated by a straight line M in a region where a light beam reflected from the optical disk 5 passes. The straight line M is a straight line that passes through the optical axis of the light beam and is parallel to the radial direction.

  The two division parts 2A and 2B are formed with a hologram pattern that guides the return light from the disk passing through the respective areas to a predetermined detector and gives astigmatism to the passing beam. . In addition, the hologram patterns of the two divided regions have two different astigmatism hologram patterns, respectively. The two different hologram patterns have different astigmatism directions, and are divided into four regions divided by a dividing line M and a virtual dividing line (dotted line N) that passes through the optical axis and is parallel to the track direction (Y direction). Are the first region 2A, the second region 2B, the third region 2C, and the fourth region 2D as shown in the figure, the directions of astigmatism in the respective regions are the first region 2A and the third region 2C. Is set in the direction of the straight line L1 in FIG. 2, and in the direction of the straight line L2 with respect to the second region 2B and the fourth region 2D.

  Referring to FIG. 2, the region on the right side of straight line M in the two divided regions has two astigmatism hologram patterns having axes in the direction of L1 in first region 2A and L2 in fourth region 2D. . On the other hand, the region on the left side of the straight line M in the figure has an astigmatism hologram pattern having an axial direction of L2 in the second region 2B and L1 in the third region 2C. The straight line L2 is set so that the angle between the straight line L2 and the dotted line N parallel to the track direction is between 0 degrees and 45 degrees, while the straight line L1 has an angle of 0 degrees with the straight line M parallel to the radial direction. It is set between 45 degrees.

  The reflected light from the optical disk divided in each region is guided to the light receiving element 6. As shown in FIG. 2, the light receiving element 6 has a configuration in which two two-divided detectors 6A and 6B separated by a separation band 8 are arranged along the radial direction. The light receiving element is arranged in the vicinity where the light beam becomes a minimum circle of confusion, and the direction of the boundary line Ld of the two-divided detector is provided along the radial direction (Y direction). Here, the two-divided detector means the detector 6A or 6B having two regions electrically separated from the boundary line Ld.

  The light divided by the first region 2A and the fourth region 2D is detected by the two-divided detector 6A. The beam shape shown in FIG. 2 shows a case where it is in a focused state. At this time, the first region 2A is detected on the left side 6AA of the two-divided detector 6A, and the fourth region 2D is detected on the right side 6AB. Similarly, the light divided by the second area 2B and the third area 2C is detected by the light receiving element 6B, the second area 2B is detected by the left side 6BA of the 2-division detection 6B, and the third area 2C is detected by the right side 6BB.

  FIG. 3 shows changes in the beam shape on the two-divided detector 6A when in the defocused state. 3A and 3B show a positive (plus +) state in which the distance between the disc and the objective lens is larger than that at the focal point, and in the state of FIGS. 3D and 3E, the focal point is obtained. This represents a negative (minus −) state that is closer to the case of FIG. FIG. 3C shows a beam shape in a focused state.

  In the plus + defocus state, the return light from the fourth region moves on the boundary line Ld of the two-divided detector. The beam shape of the light in the first region changes in the left detector of the two-divided detectors. As the defocus approaches 0 from zero, the difference in intensity between both detectors will approach zero. Unlike the conventional method, the shape of the beam is not a straight line but bent into a “<” shape at the front and rear focal points of astigmatism.

  On the other hand, in the negative defocus state, the return light from the first region moves along the boundary line Ld of the two-divided detector. Similarly, the difference in intensity between the left and right detectors approaches zero as it approaches zero from minus. In the defocused state on the + side and − side, the strong side is switched in the two-divided detector. Therefore, by taking the difference, a focus error signal can be obtained.

In the optical pickup according to the present embodiment, when the output signals of the light receiving elements 6AA, 6AB, 6BA, and 6BB are I _6AA , I _6AB , I _6BA , and I _6BB , the focus error signal is obtained by the astigmatism method (I _6AA + I _6BB ) − (I _6AB + I _6BA ). FIG. 4 is a diagram showing the relationship between the change in the distance between the disc and the objective lens and the FES signal intensity. In FIG. 4, a solid line S1 indicates a calculation result of a focus error signal, that is, a so-called S curve in the method according to the present embodiment. A dotted line S2 indicates an S curve by the astigmatism method in the conventional example.

On the other hand, the tracking error signal (push-pull signal) is generated by the calculation of (I _6AA + I _6BA ) − (I _6AB + I _6BB ). In addition, the hologram pattern of the present embodiment can also detect a tracking error signal by the DPD method. In the DPD method, a tracking error signal is detected by a phase difference between light intensities received by each detector. That is, a tracking error signal by DPD is obtained by Phase {(I _6AA + I _6BB ) − (I _6AB + I _6BA )}. In the above formula, Phase indicates that the phase difference of each intensity is taken. Since the phase difference generated varies depending on which position of the light beam the pit formed on the optical disk 5 passes, the track position information can be obtained by obtaining this phase difference. When the light beam passes through the center of the track on the optical disc 5, the phase difference is zero. That is, in the optical pickup according to the present embodiment, tracking servo is performed by moving the objective lens 4 so that the phase difference becomes zero.

  Next, the effect of suppressing the leakage of the track cross signal to the focus error signal by using this embodiment will be described with reference to FIGS. Looking at the light spot on the detector in the present embodiment, as shown in FIG. 2, the two fan-shaped shapes formed of ¼ circles are in contact with each apex angle. . On the other hand, the light spot by the conventional astigmatism method has a semicircular shape, and it is assumed that the two ¼ sectors are in contact with each other along a straight line parallel to the boundary line of the two-divided detector. (See FIG. 8). Comparing the two, the movement between the detectors of the push-pull component accompanying defocusing can be made more gradual when they are far away. Also, by suppressing the spread of the intensity distribution near the boundary line of the two-divided detector, it is possible to suppress the change in the intensity distribution with respect to the deviation of the center of the light spot on the detector. Can be suppressed. For this reason, the crosstalk mixed in FES can be suppressed.

  FIGS. 5A and 5B show the simulation results. In the figure, Q1 is the one in which the astigmatism direction L1 is set to 22.5 degrees and L2 is set to 67.5 degrees with respect to the dividing line M. Q2 is set to set L1 to 32.5 degrees and L2 to 57.5 degrees. Q3 shows the result of the normal astigmatism method in which both L1 and L2 are set to 45 degrees (S2 in FIG. 4). The light spot at the focal point on the photodetector in each case is, in the case of Q1, the angle between two ¼ circles that are aligned with their apex angles facing each other, exactly 90 degrees. It becomes. The case of Q3 is a conventional semicircular case, and the angle formed by the fan shape (acute angle side) is assumed to be 0 degree. The angle formed by the sector in the case of Q2 (acute angle side) is an angle between Q1 and Q3. As an optical disk, a track pitch of DVD-RAM is assumed.

  FIG. 5A shows the track cross signal with respect to the degree of defocus (horizontal axis) when there is a deviation of 30% in the track direction (direction perpendicular to the boundary line of the two-divided detector) with respect to the beam radius. This represents the size (vertical axis). The defocus positions T1, T2, and T3 on the horizontal axis indicate the positions of T1, T2, and T3 shown in the S curve curve of FIG. As shown in the figure, it can be seen that the track cross signals of Q1 and Q2 of the embodiment of the present invention are smaller than Q3 using the conventional semicircular beam shape.

  FIG. 5B shows the magnitude of the track cross signal with respect to the change in the deviation in the track direction (horizontal axis) when there is a constant defocus amount. Also in this evaluation, it can be seen that the astigmatism method of the present invention is more effective in suppressing crosstalk than the conventional astigmatism method.

  By setting the hologram pattern as in the present embodiment as described above, even when the light spot on the detector has a spot shift in the track direction, that is, in the direction perpendicular to the boundary line of the two-divided detector, Since FES crosstalk can be suppressed, more stable focus servo can be performed.

  Further, the direction and magnitude of the astigmatism to be applied may be different in each region. For example, L1 is 22.5 degrees, L2 is 67.5 degrees with respect to the first region and the fourth region, respectively. If L1 is set to 32.5 degrees and L2 is set to 57.5 degrees with respect to the second area and the third area, the light spot on the detector has a shape as shown in FIG. By adopting such a shape, the sensitivity of the S curve can be optimized.

  Further, the optical pickup according to the present embodiment has a configuration in which the diffraction efficiency of the light beam passing through the hologram element 2 changes depending on the polarization state of the light beam incident on the hologram element 2. Is more preferable.

  When the hologram element 2 is one in which the diffraction efficiency of the light beam passing through the hologram element 2 varies depending on the polarization state of the light beam incident on the hologram element 2, for example, the light beam emitted from the semiconductor laser 1 The light beam reflected from the optical disk 5 can be diffracted. Therefore, for example, since the hologram element 2 can be disposed between the semiconductor laser 1 and the optical disk 5, the size of the optical pickup device can be reduced. Further, since the presence or absence of diffraction can be changed depending on the polarization state of the light beam incident on the hologram element 2, it is possible to suppress the loss of the amount of light reaching the optical disc 5. For this reason, since a strong light beam can be irradiated to the optical disc 5, information can be recorded on the optical disc 5 at high speed.

  In the above-described embodiment, the configuration has been described in which the astigmatism directions of the hologram pattern are alternately changed so that the adjacent areas do not have the same astigmatism direction with two different astigmatism directions. However, the hologram pattern is not limited to the above-described configuration, and any hologram pattern may be used as long as the divided areas on adjacent diffraction elements are separated without linear contact in the detection unit.

  Next, a comprehensive embodiment of the optical pickup of the present invention is listed, including the configuration shown in the embodiment of the present invention.

  It is desirable that none of the directions of the plurality of astigmatisms of the hologram pattern in the plurality of regions of the diffraction element be orthogonal to each other. With this configuration, the spot from each hologram pattern in the diffraction element can be separated at the in-focus position.

  In the diffraction element described above, the astigmatism directions of the hologram patterns in the divided areas adjacent to each other can be made different. With this configuration, the quarter circle spots at the focal point can be separated from each other.

  The light receiving element may include two two-divided detectors. With this configuration, the advantages of the present invention can be obtained while using the conventional astigmatism method.

  It is desirable that the diffractive element has polarization characteristics. With this configuration, the diffraction efficiency changes depending on the polarization state of the light beam passing through the diffraction element. Therefore, the light beam reflected from the recording medium is transmitted to the recording medium side while the light beam emitted from the semiconductor laser of the light source is transmitted to the light receiving element. Can be diffracted. In addition, the loss of the light beam that passes through the diffraction element toward the recording medium can be suppressed.

  The diffraction element, the light source, and the photodetector can be integrated. With this configuration, the optical pickup can be reduced in size.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  By using the optical pickup of the present invention, it is possible to stably perform high-quality recording / reproduction on various information recording media with reduced crosstalk and the like, which brings about a useful improvement.

It is a side view which shows the schematic structure of the optical pick-up apparatus in this Embodiment. It is a top view explaining the planar positional relationship of the hologram pattern of the hologram element in this Embodiment, and the light-receiving part which receives the light divided | segmented by the said hologram pattern. It is a figure which showed the change of the light beam spot by the degree of defocusing on a detector, and each is defocused when (a) is ++, (b) is +, (c) is zero. In the case of (focus), (d) shows the case of-, and (e) shows the case of-. It is a figure which shows the S curve which shows the relationship between the degree of a defocus, and a focus error signal. It is a calculation result which shows the magnitude | size of the crosstalk to the focus error signal in the prior art example in an astigmatism method, and the Example of this invention, (a) is the influence of a defocus degree, (b) is a center shift | offset | difference. It is a figure which shows the influence of. It is a figure which shows the light beam spot on the detector in another structure of this Embodiment. It is a side view which shows the schematic structure of the conventional optical pick-up apparatus. It is a figure which shows the planar positional relationship of the hologram element and light receiving element in FIG. In the conventional astigmatism method, it is the figure which showed the shape change of the light beam at the time of defocusing, respectively, when a defocus is (++), (b) is +, (c) is zero. In the case of (focusing point), (d) shows the case of-, and (e) shows the case of-. It is a figure explaining the factor which crosstalk produces in the conventional astigmatism method, (a) shows the case where a spot center exists on a boundary line, (b) shows the case where a spot center deviates from a boundary line, (c) Indicates an FES signal in which a track floss signal is generated.

Explanation of symbols

  1 light source, 2 hologram element (diffraction element), 2A, 2B, 2C, 2D hologram element area divided by dividing line, 3 collimating lens, 4 objective lens, 5 optical disk, 6 detector, 6A, 6B detector Area, 6AA, 6AB part of 6A divided by boundary line, 6BA, 6BB part of 6B divided by boundary line, 7 light beam, 8 separation band between two two-divided detectors, L1, L2, H1 Astigmatism direction, boundary line of Ld 2 split detector, split line of M hologram element, split line of N hologram element (perpendicular to M), S1, S2 S curve indicating relationship between FES signal intensity and degree of defocus , T1, T2, T3 Defocus degree.

Claims (7)

A light source that emits a light beam, a light condensing element that condenses the light beam on an optical recording medium, and a light source and a light condensing element that are disposed between the light source and the light condensing element. In an optical pickup comprising a diffractive element that divides into a beam and a detector having a light receiving element that receives the light beam divided by the diffractive element,
Each of the diffractive elements has a plurality of divided regions each having a hologram pattern that generates astigmatism, and the plurality of light beams diffracted in the respective regions cause light spots to be located at different positions on the detection unit. The astigmatism direction in which the hologram pattern is generated in one area among the plurality of areas of the diffraction element is different from the astigmatism direction in which the hologram pattern is generated in at least one of the other areas. Features an optical pickup.   2. The optical pickup according to claim 1, wherein none of a plurality of astigmatism directions of a plurality of hologram patterns of the diffraction element are orthogonal to each other.   3. The optical pickup according to claim 1, wherein in the diffraction element, directions of astigmatism of hologram patterns in regions adjacent to and in contact with each other are different. A light source that emits a light beam, a light condensing element that condenses the light beam on an optical recording medium, and a light source and a light condensing element that are disposed between the light source and the light condensing element. In an optical pickup comprising a diffraction element that diffracts into a beam, and a detection unit that includes a light receiving element that receives a plurality of light beams diffracted by the diffraction element,
The diffraction element has four hologram patterns that generate astigmatism, respectively, corresponding to four regions divided by two intersecting dividing lines,
The optical pickup is characterized in that the four hologram patterns are diffracted so as to form four light spots separated from each other in a focused state in the detection unit.   The optical pickup according to claim 1, wherein the light receiving element has two two-divided detectors.   6. The optical pickup according to claim 1, wherein the diffraction element has a polarization characteristic.   The optical pickup according to claim 1, wherein the diffraction element, a light source, and a photodetector are integrated.

Images